The equation of state for stellar envelopes. III - Thermodynamic quantities

Daêppen, W.; Mihalas, Dimitri; Hummer, D. G.; Mihalas, B. W.

doi:10.1086/166650

Cited by 229 publications

(129 citation statements)

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“…The cross-sections and level populations needed for the absorption and scattering coefficients then depend only on the gas density ρ and the temperature T . Microscopic plasma thermodynamics is treated with the Mihalas-Hummer-Däppen equation of state (EOS) for stellar envelopes Mihalas et al 1988;Däppen et al 1988;Mihalas et al 1990) and used in tabulated form. The solar chemical composition for the 15 elements included in the EOS and for the opacities is taken from the abundances of Asplund et al (2005).…”

Section: Absorption and Scattering Opacity Sources In The Sunmentioning

confidence: 99%

Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Hayek

Asplund

Carlsson

et al. 2010

A&A

147

174

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Aims. We present the implementation of a radiative transfer solver with coherent scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD) simulations of stellar surface convection. The code is fully parallelized using MPI domain decomposition, which allows for large grid sizes and improved resolution of hydrodynamical structures. We apply the code to simulate the surface granulation in a solar-type star, ignoring magnetic fields, and investigate the importance of coherent scattering for the atmospheric structure. Methods. A scattering term is added to the radiative transfer equation, requiring an iterative computation of the radiation field. We use a short-characteristics-based Gauss-Seidel acceleration scheme to compute radiative flux divergences for the energy equation. The effects of coherent scattering are tested by comparing the temperature stratification of three 3D time-dependent hydrodynamical atmosphere models of a solar-type star: without scattering, with continuum scattering only, and with both continuum and line scattering. Results. We show that continuum scattering does not have a significant impact on the photospheric temperature structure for a star like the Sun. Including scattering in line-blanketing, however, leads to a decrease of temperatures by about 350 K below log 10 τ 5000 < ∼ −4. The effect is opposite to that of 1D hydrostatic models in radiative equilibrium, where scattering reduces the cooling effect of strong LTE lines in the higher layers of the photosphere. Coherent line scattering also changes the temperature distribution in the high atmosphere, where we observe stronger fluctuations compared to a treatment of lines as true absorbers.

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Section: Absorption and Scattering Opacity Sources In The Sunmentioning

confidence: 99%

Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Hayek

Asplund

Carlsson

et al. 2010

A&A

147

174

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“…However, its range of validity does not cover either the electron degenerate cores of RGB stars or their cooler, most external layers, below 5000 K. RGB models computed with the OPAL EOS must employ some other EOS to cover the most external and internal stellar regions. As for the models discussed later, Caloi, D'Antona, & Mazzitelli (1997) and Silvestri et al (1998) use the MHD (Däppen et al 1988) EOS below 5000 K, while the Magni & Mazzitelli (1979) one is used for the cores; Salaris & Weiss (1998, hereafter SW98) and Cassisi et al (1998) complement the OPAL EOS with the Straniero (1988) one for the degenerate cores and a Saha EOS for the most external layers, while the Yale-Yonsei models (Yi et al 2001, hereafter YY01) employ the Yale EOS (e.g., Chaboyer & Kim 1995) for regions outside the range of validity of the OPAL data. The widely used Padova models by Girardi et al (2000, hereafter P00) employ their own implementation of the Straniero (1988) EOS for K (Girardi et al 1996) and the MHD EOS at lower 7 T 1 10 temperatures.…”

Section: Equation Of Statementioning

confidence: 99%

Red Giant Branch Stars: The Theoretical Framework

Salaris

Cassisi

Weiß

2002

PUBL ASTRON SOC PAC

179

172

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ABSTRACT. Theoretical predictions of red giant branch stars' effective temperatures, colors, luminosities, and surface chemical abundances are a necessary tool for the astrophysical interpretation of the visible-near-infrared integrated light from unresolved stellar populations, the color-magnitude diagrams of resolved stellar clusters and galaxies, and spectroscopic determinations of red giant chemical abundances. On the other hand, the comparison with empirical constraints provides a stringent test for the accuracy of present generations of red giant models.We review the current status of red giant star modeling, discussing in detail the still-existing uncertainties affecting the model input physics (e.g., electron conduction opacity, treatment of the superadiabatic convection) and the adequacy of the physical assumptions built into the model computations.We compare theory with several observational features of the red giant branch in Galactic globular clusters, such as the luminosity function "bump," the luminosity of the red giant branch tip, and the envelope chemical abundance patterns, to show the level of agreement between current stellar models and empirical data concerning the stellar luminosities, star counts, and surface chemical abundances.

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“…To match the simulations, we use the MHD equation of state (EOS) [14][15][16]. To cover the necessary range of temperatures, we complement it with OPAL EOS [17] at higher temperatures.…”

Section: Important Remarksmentioning

confidence: 99%

Improving 1D Stellar Models with 3D Atmospheres

et al. 2017

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Abstract. Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature -also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

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The equation of state for stellar envelopes. III - Thermodynamic quantities

Cited by 229 publications

References 0 publications

Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres

Red Giant Branch Stars: The Theoretical Framework

Improving 1D Stellar Models with 3D Atmospheres

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